Quote: "i'm only looking forward to Dark GDK bcz its open source "
Where did you read this? As far as I can follow the newsletters, Dark Basic Pro and FPS Creator are open-source (fully or partially, I don't really know), but not Dark GDK.
Quote: "I'm new to this Dark GDK engine"
Quote: "now a days Engines are meant for this purposes"
Just to be clear, Dark GDK is not an engine. It is a collection of functions that wrap DirectX functionality, to make it easier to use. That means you don't need to worry about native DirectX calls, like getting a device context, for example, but (as with any high-level wrapper functionality) it is an additional layer between you and the system. It has a defined set of functions which, to some extent, limit what you can do. This may or may not be enough for your purpose.